A Thermal Protection System (TPS) is used to provide heat shielding for the payload and structure of aerospace vehicles traveling at hypersonic speeds in atmospheric environments such as during launch or reentry into the earth's atmosphere or entry into the Martian atmosphere. There are two principal TPS types: reusable (as used for the Shuttle) and ablative (as used for planetary entry probes). For a reusable TPS, typically used for mild entry environments, the mass and properties of the TPS are not changed. On the other hand, an ablative TPS protects the vehicle using a thermo-chemical process, such as an ablation process that lifts the hot shock gas layer away from the vehicle, heat absorption which protects the vehicle through ablation of the TPS material, and creation of a char layer which is both an effective insulator and an effective radiant heat shield from the shock layer.
Lightweight ablation materials include phenolic impregnated carbon ablator (PICA), as developed by NASA Ames and used in the Stardust Sample return mission, PICA-X developed by SpaceX for the Dragon space capsule, Silicone Impregnated Reusable Ceramic Ablator (SIRCA) developed by NASA Ames and used on the back shell of the Mars Pathfinder, Superlight Ablator (SLA) particularly SLA-561, a proprietary ablative material made by Lockheed Martin that is the primary TPS material on the 70 degree sphere-cone entry vehicles sent to Mars by NASA, and Avcoat manufactured by HR Textron. Each of these materials requires characterization during testing, and for various reasons is challenging to characterize for temperature profile. Prior art measurement systems typically use thermocouples for this purpose, with one thermocouple used for each measurement. A disadvantage of this approach is that each discrete thermocouple requires its own aperture and penetration into the material, and a large number of measurements results in a large number of thermocouple ingresses and egresses. The thermocouple wire itself is formed from metallic wire, and therefore has a significantly different thermal conductivity than the TPS material which surrounds it. Accordingly, the large number of ingresses and egresses of conductive wire each represent a discontinuity in the insulating material, thereby contributing to measurement inaccuracy. It is desired to provide a single string-like sensor with a plurality of sensors fabricated along the string, thereby providing a large number of temperature measurements with a minimum number of ingresses and egress.